Shared Neutrals on 8 circuit 12/14 multi-question

[variable]

I have 8x750w S4 lekos patched into 4 dimmers via an 8 circuit 12/14 multi-cable. I'm trying to patch more lights on the same electric and am considering doubling up the S4s into the 1st 4 circuits of the multi-cable.

My first question is capacity, can anyone think of a reason that 2 750w Source Fours would be problematic in an 8 circuit setup given that each circuit is sharing a neutral with another circuit?

Second, the dimmer has 3 phase power and the instruments I want to power are from a different dimmer entirely that's powered by a single 120v 20a source. I can't find a wiring diagram for putting 8 channels on a 12/14 socapex so does anyone know how the neutrals are wired so I can make sure that I'm keeping the power sources separate?

Am I overthinking this?

Finally, does anyone know a licensed electrician in the San Francisco Bay Area with a lot of experience in theatre installations? Our last electrician just retired and his replacement has no experience with theatrical installations.

Thanks in advance.

 

[afreeradical]

The 1st question I have is what capacity are your dimmers... If they are 1.2Kw then NO you can't...
Second question... 12/14 ? is this a 12 AWG cable with 14 conductors ? I could just be tired... This end of a long week for me....
But that's a standard 6 circuit socapex.... So to have 8 on it already 2 of the fixtures must be twofered.... (So your dimmers must be larger than 1.2K unless you have 575W bulbs in lamps and don't realize it)
Also not sure what you mean by
"an 8 circuit setup given that each circuit is sharing a neutral with another circuit?" because that's NOT how socapex is wired....

Each circuit on the 12awg soca is good for roughly 1800W and has it's own Hot and Neutral with shared grounds...so if you make Twofers and your dimmers can handle it you could double up all 6 circuits.
But you should only be able to dim 6 circuits on 6 dimmers with 2 lamps on each Circ/Dim.. unless someone has done something to the socapex, then your into a whole different ball of wax and if you don't understand what's been done... You shouldn't be messing with it.....

"Second, the dimmer has 3 phase power and the instruments I want to power are from a different dimmer entirely that's powered by a single 120v 20a source. I can't find a wiring diagram for putting 8 channels on a 12/14 socapex so does anyone know how the neutrals are wired so I can make sure that I'm keeping the power sources separate?"

This I don't understand At All.... Not sure how your connecting a Socapex to 2 different dimmer racks unless your whipping it out at the dimmer end.....
If this is the case and nobody has REWIRED your standard socapex then this is not an issue....
If your socapex Has been altered somehow so your controlling 8 circuits with a 6 Circuit socapex then it may be a very big problem and I could not advise without actually opening the socapex and seeing what someone has done....

Hope that helped somewhat...

 

[BillConnerFASTC]

You really shouldn't use shared neutrals on dimmed stage circuits for all sorts of reasons, chief too easy to not be close to balanced. The socapex cable should be used for 6 circuits. You could really hurt the next person who - like most of us - would never expect it to be used for 8 with shared neutrals.

I think this falls into if you can't do it correctly, don't do it.

 

[derekleffew]

... Each circuit on the 12awg soca is good for roughly 1800W and has it's own Hot and Neutral with shared grounds...so if you make Twofers and your dimmers can handle it you could double up all 6 circuits. ...

Remember also that Socapex cable and infact all multi-cable requires diversity, electrical , a derating, in this case 50%, of the six 20A circuits, if one intends to use all circuits at full intensity.

 

[variable]

I've got paperwork from the house I bought the cable from saying it's 12/14, but it doesn't seem likely based on the responses here. I'm going to have to open the plugs and find out what I've really got. Unfortunately the cable is old enough that no legible markings remain on the cable itself. It is an 8 channel multi, not a 6. I read a few discussions here where people were discussing shared neutrals in multi cable, but if it's really not standard I think it's unlikely that a cable I bought from a rental house did that.

That said, shared neutrals are the bane of the house I'm working in. All the old circuits that were wired in the 80s are doubled to share a neutral back to the dimmer and keeping them straight (and from being overloaded--it's too easy for a designer to dump 4kw of lights on a 14AWG wire) is a nightmare. That's probably why I rushed to the conclusion that I've got shared neutrals in the multi. It sounds like it's probably NOT 12/14, but 14/19. or something lighter. 14g should be fine to share 1500w (unless there's something about multi cable I need to know).

Thanks for the feedback.

 

[variable]

Remember also that Socapex cable and infact all multi-cable requires diversity, electrical , a derating, in this case 50%, of the six 20A circuits, if one intends to use all circuits at full intensity.

Could you explain in a little more detail about derating? It sounds like you mean that I should have wire with double the capacity of the power I'm pushing through them.

 

[derekleffew]

Ampacity ratings for cable are for a single wire in free air. When cable/wires are inside a conduit or jacket, the number of current carrying conductors (both hots and neutrals but not grounds) determine a factor that must be applied as more conductors means more heat.

From the wiki entry diversity, electrical :

Electrical diversity is a calculation used in determining the amount of power feeding a system or the size of a multi-circuit cable. 50% diversity means that half the circuits are loaded, or all the circuits are loaded to half their rating. It can also mean that only half the fully loaded circuits are energized simultaneously.

 

[STEVETERRY]

Remember also that Socapex cable and infact all multi-cable requires diversity, electrical , a derating, in this case 50%, of the six 20A circuits, if one intends to use all circuits at full intensity.

Derek is right. However, somehow the link to the article got broken, which I have fixed.

This is the link:

http://www.etcconnect.com/uploadedF...Understanding_Hidden_Electrical_Diversity.pdf

ST

 

[STEVETERRY]

Could you explain in a little more detail about derating? It sounds like you mean that I should have wire with double the capacity of the power I'm pushing through them.

Have a read through the article (link just fixed), and then let us know if you have questions!

http://www.etcconnect.com/uploadedF...Understanding_Hidden_Electrical_Diversity.pdf


ST

 

[STEVETERRY]

I have 8x750w S4 lekos patched into 4 dimmers via an 8 circuit 12/14 multi-cable. I'm trying to patch more lights on the same electric and am considering doubling up the S4s into the 1st 4 circuits of the multi-cable.

My first question is capacity, can anyone think of a reason that 2 750w Source Fours would be problematic in an 8 circuit setup given that each circuit is sharing a neutral with another circuit?

Second, the dimmer has 3 phase power and the instruments I want to power are from a different dimmer entirely that's powered by a single 120v 20a source. I can't find a wiring diagram for putting 8 channels on a 12/14 socapex so does anyone know how the neutrals are wired so I can make sure that I'm keeping the power sources separate?

Am I overthinking this?

Finally, does anyone know a licensed electrician in the San Francisco Bay Area with a lot of experience in theatre installations? Our last electrician just retired and his replacement has no experience with theatrical installations.

Thanks in advance.

Let's be clear on a few key issues:

1. The world standard for 12/14 multicable is six circuits, not eight.

2. While shared neutrals are technically possible on multicable (although never desirable--for a number of reasons beyond the scope of this thread) they are never allowed on multicable with cord-connected feeds (male connectors) of single circuits!
Why not?
With single-circuit cord connected feeds, there is no guarantee that circuits with a shared neutral will be on different phases. the result will be severe overcurrent, and a fire hazard.

3. Finally, per NEC section 210.4 (B), all multiwire (shared neutral) circuits require a common means of disconnect. This is not likely or generally possible in entertainment lighting systems.

Please read this article about diversity and multicable loading:
http://www.etcconnect.com/uploadedF...Understanding_Hidden_Electrical_Diversity.pdf



ST

 

[afreeradical]

Thanks Derek and Steve, I did want to get into that and meant to mention about derating and not running lamps at full if this is done...because not recommended...
but got caught up trying to figure out how he was connecting a soca to more than 1 rack with shared neutrals...
Then lunch was almost over and had to rush through the post and get back for my evening show....
A most important thing to unfortunately miss
I use 575W bulbs which keeps me close to the derating, plus with the way I circ my rig... rarely would I run all 6 at same time and wouldn't be running them at full if I knew I'd doubled all 6 circ's up for some odd reason''''
I had a lot more I was going to go into but thoughs articles pretty much say it all, which is good because I think what he has maybe very unsafe.
But with the crappy internet I have in my booth, this is the 4th time I've tried to post, finally had to type out on a note pad and copy paste

 

[MikeJ]

12/14 share Grounds, but should not share neutrals. Also, look up the manufactures rating on cables, this may be hard with old and poorly marked cables, and even though academic arguments about free air, vs. in conduit, vs. multi de-rating might be entertaining on the internet, an good to know if applicable to your job, some of us have real actual work to do, and following the manufactures spec is the easiest way to go, and know you are operating safely.

 

[STEVETERRY]

12/14 share Grounds, but should not share neutrals. Also, look up the manufactures rating on cables, this may be hard with old and poorly marked cables, and even though academic arguments about free air, vs. in conduit, vs. multi de-rating might be entertaining on the internet, an good to know if applicable to your job, some of us have real actual work to do, and following the manufactures spec is the easiest way to go, and know you are operating safely.

Hmmm...

These discussions about allowable loading on a multiconductor cable are hardly "academic arguments" that are just "entertaining on the internet". Derating and diversity are mandated by the National Electrical Code, and should be part of every entertainment electrician's body of knowledge. Only the base ampacity of a cable gauge/temperature rating is likely to be covered in manufacturer data sheets--and that is not enough to insure a safe use of a multi-circuit cable where the manufacturer makes no assumptions about the number of current-carrying conductors in the cable.

That is why the NEC is an invaluable tool that should be in every electrician's toolbox. The contents of the NEC are applicable and important to every entertainment electrician's job.

For those with "real work to do" knowledge of the NEC on these issues is essential. Don't take my word for it--look at the scope of the ETCP exam-- an ETCP certification is the most definitive measure of "qualified personnel" in the entertainment industry.

ST

 

[variable]

Let's be clear on a few key issues:

1. The world standard for 12/14 multicable is six circuits, not eight.

2. While shared neutrals are technically possible on multicable (although never desirable--for a number of reasons beyond the scope of this thread) they are never allowed on multicable with cord-connected feeds (male connectors) of single circuits!
Why not?
With single-circuit cord connected feeds, there is no guarantee that circuits with a shared neutral will be on different phases. the result will be severe overcurrent, and a fire hazard.

3. Finally, per NEC section 210.4 (B), all multiwire (shared neutral) circuits require a common means of disconnect. This is not likely or generally possible in entertainment lighting systems.

Please read this article about diversity and multicable loading:
http://www.etcconnect.com/uploadedF...Understanding_Hidden_Electrical_Diversity.pdf

ST

Hi Steve. Thanks for clearing that up. I have no intention of changing or building any multi cable, I was just erroneously assuming something about the cable that I apparently had no reason to assume, not knowing my multi cable very well. Ironically my main reason for putting the multi-cable up was to relieve the load on my aging grid which is all paired circuits with shared neutrals, many of which have been fried to a crisp by trying to support 4kw worth of PAR can. I don't trust any of them so I'm doing what I do on location and find a good electriician to set me up with power and just run cable to the lights.

I'm more nervous than ever about [HASHTAG]#3[/HASHTAG] above. I've literally got 75 odd 750w & 1kw lights going through about 50 circuits that are sharing neutrals back to a box where they fork out so they can plug into 3 12 ch dimmer packs each of which have a 3 phase power supply and their own 100amp breaker.

 

[MikeJ]

@STEVETERRY Don't misunderstand me. The appropriate application of equipment is quite important, but it seems these discussions often lead to gross generalizations, of people trying to show how smart they are and providing no particularly useful information.

You'r link, on the other hand, like I mentioned in a previous post, is a manufacturer offering real world use, and specific application for our industry. Knowing what is to code is important, almost important as knowing what is safe, but knowing the codes for obscure applications that mostly never arise in real world workplaces is not as useful, IMO

Thank you for the link.

Out of curiosity, I may email LEX tomorrow and ask what the rated capacity of their 12/14 Soca cable is, with all circuits in use.
It would seem silly to not know the how many current carrying conductors are in a cable that they manufacture, or what the maximum rating is, when all conductors are utilized. But I guess you never know, but hat's why I am here; to learn, and help where I can.

 

[BillConnerFASTC]

I worry a little that the multiconductor diversity allowed by the NEC was based on a border light or plug strip, where I suspect there is a high level of diversity, with some circuits never loaded. I worry about that premise when running 6 circuit cables with socapex. The first is often a permanent install with some conservative design built in. The second seems more often production specific. Not today so much but I'd guess there were lots of 6 circuit cables with a pair of 1k pars on each circuit and while not continuous by code, still on a lot.

Does come down to competent people who understand how to do things safely and not just max out every sub-part and exception in the code.

 

[JD]

"home run" of each circuit is important for more than just loading applications. Lets say you have two circuits on two different phases feeding two fixtures sharing a neutral. Works fine, right? Well, what happens if the neutral is lost at the connector or other location? You shut off circuit "A" to work on the connector feeding fixture A.... Surprise! The circuit is still hot due to potential power feeding circuit B making it's way back through fixture B. This is why in any application where a neutral is shared or there are multiple hots feeding a device (like a motor), all of the hots must be broke at the same time, thus the common handle on a three phase breaker.

rant:
Now I just wish the code book would apply INSIDE of equipment as well! Sick of seeing 2 pole breakers used on three phase motors, leaving the windings hot 24/7.
/rant

 

[variable]

Let's be clear on a few key issues:

Please read this article about diversity and multicable loading:
http://www.etcconnect.com/uploadedF...Understanding_Hidden_Electrical_Diversity.pdf

That was a really useful article. I contacted the rental house I bought that cable from and their best guess is also that I've got 14AWG/19 conductor running 8 circuits. Given that, and the article above, my capacity is 120A but the ampacity adjustment should lower that to 84A given the 70% figure on table 520.44. Since I'm only running 8 750w instruments (52ish amps at 115v) right now, I could double those up on four circuits providing I don't put more than 31 amps on the 4 open circuits.

Does that sound right?

 

[JD]

Actually, 14/19 sounds very odd. Soca is a 19 pin connector, but the center pin, [HASHTAG]#19[/HASHTAG] is not used. The usual is to have 6 hots, 6 neutrals, and 2 grounds. That of course comes to 14 conductors, so the original 12/14 sounds more on the money. Still a six circuit cable. I would look very carefully at the jacket of the cable for either a breakdown number or a manufacturer and identifier number. If you find the later, google it and see if you can find out the real conductor number. It might be 19, but you need to know for sure. In any case, there is a very distinct layout for the pins on 6 circuit Soca cables, so it there is an 8 connector breakout and 8 circuits running through it, I would be very concerned. You would be asking for trouble if you happened to rent in some extra equipment in the future.

 

[MikeJ]

I have come across 14/19, or maybe even 16/19, but its not real common. The main reason to use 19 conductor is for audio, and typically 12ga cable is the minimum for speaker cable. And just to be diligent, if you use soca for speaker cable, it is often backwards, so the female end is at your rack, to avoid the lighting guy plugging it into a PD, and sending a 60hz tone to your speakers, but maybe not for very long. care still needs to be taken though, the output from an audio amp can still be fatal.

You could always take the shell of the connector and look at how its wired, or just meter the ground pins. If they have continuity to each other, it is a 14 wire cable, if they do not, but each ground has continuity from end to end than it is a 19 conductor. If any of the ground pins show no continuity, end to end, and none between pins, than its wired wrong to begin with.